This is a competitive renewal application of a project initially designed to define mechanisms of cardiac myocyte dysfunction that leads to heart failure, a significant health problem in the US. Work in previous funding cycles has shown that cardiac diseases cause abnormalities in intracellular Calcium regulation and myocyte contractility. These abnormalities lead to cell death, and reduction in the number of functional cardiac myocytes. The major goal of the proposed research is to test/develop novel cell-based approaches to repair the heart after myocardial infarction (MI). The idea is that cardiac structura and functional decline after MI can be reduced or corrected using cell therapy. The Aims are to 1) Determine if/how enhancing Cn43 expression in cardiac (CSC) or compact bone derived stem cells (CBSCs) enhances their survival, engraftment and differentiation into new cardiac tissue when injected into the infarct border zone after MI~ thus increasing their capacity to improve post-MI cardiac structure and function~ and 2) Determine the role of ?1G T-type Ca2+ channels (TTCCs) in the generation of new myocytes derived from either CSCs or proliferative cardiac myocytes after MI. Our recent work shows that CBSCs are a novel cell with the capacity to improve cardiac function in mouse MI models. The new work will define the mechanisms (differentiation into new cardiac tissue and/or enhancing endogenous repair of the native heart) of CBSC-mediated repair. A novel lineage tracing approach will be used to unambiguously examine these issues. These studies will also determine if enhancing Cn43 coupling of CBSCs and cardiac myocytes enhances stem cell survival and differentiation into new cardiac myocytes. Our recent work also shows that TTCCs regulate stem cell proliferation and commitment to the cardiac lineage. In Aim 2 studies we will determine if modulation of TTCCs in cKit+ CSCs alters the ability of these cells to form new cardiac myocytes after MI. Finally we will perform proof of concept experiments without most efficacious cells (defined in mice) in a pig MI model, to document that the strategies being developed have the potential to translate to patients with ischemic heart disease.